JP4868065B2 - Frequency division multiplex transmission equipment - Google Patents

Description

  The present invention relates to frequency division multiplex transmission. The present invention relates to an orthogonal frequency division multiplex transmission system (ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING transmission system: OFDM transmission system) and an orthogonal frequency division multiplex access transmission system (ORTHOGONAL FREQUENCY DIVISION MULT CCLEX transmission system) in which adjacent carrier frequencies are arranged in an orthogonal state. This is a useful invention when using the OFDMA transmission system.

  IEEE 802.11 (WiFi), IEEE 802.16 (WiMAX), 3.9th generation wireless access network communication (SUPER3G), 4th generation wireless access are communication systems that employ frequency division multiplexing transmission such as OFDM transmission including OFDMA. Network communication (4G) and the like can be mentioned.

  Transmission using OFDM uses an RF frequency in a wide band by multi-carrier. Further, transmission using OFDM can be resistant to frequency selective fading by using an error correction technique or the like. In a system that performs OFDM transmission, the modulation system of subcarriers constituting a multicarrier may be changed.

  On the other hand, an antenna used in a transmission apparatus or the like that performs OFDM transmission does not have a uniform standing wave ratio characteristic (Standing wave ratio characteristic: SWR characteristic) over the entire RF frequency band. Ordinary antennas generally have frequency-standing wave ratio characteristics as shown in FIG. In FIG. 1, the standing wave ratio of the center frequency is small, and impedance matching is achieved. On the other hand, as the frequency deviates from the center frequency, the standing wave ratio in FIG. 1 increases and impedance matching becomes insufficient. In order to make the antenna compatible with a wide band, there is an idea of giving a plurality of resonance frequencies to the antenna as shown in FIG. As shown in FIG. 1 and FIG. 2, when the SWR characteristic is different for the entire RF frequency band in which OFDM transmission is performed, it is affected by the frequency gain deviation. Therefore, in OFDM transmission with a wide signal band, there is a problem that it is affected by the frequency gain deviation of the antenna and feeder system as shown in FIGS. When greatly affected by the frequency gain deviation, there arises a problem that many signal identification errors occur at the opposite receiver.

Patent document 1 is known as a prior art.
JP 2002-237795 A

  An object of the present invention is to perform transmission in consideration of the influence of a frequency gain deviation of an antenna / feeder system when performing frequency division multiplexing transmission in a frequency division multiplexing transmission apparatus.

  Means for solving the above problems will be described below. In order to solve the problem, a frequency multiplex transmission apparatus that transmits and receives a frequency multiplex signal including a plurality of subcarriers includes a transmitter capable of transmitting the frequency multiplex signal by a plurality of modulation schemes, and a signal state for the frequency multiplex signal. A receiving unit that can receive from the opposite station, and a control unit that obtains a signal state for each subcarrier based on the received signal state and the frequency characteristics of the antenna in the transmitting unit, and performs transmission control based on the obtained result With.

  According to the present invention, when frequency division multiplex transmission is performed, it is possible to perform transmission in consideration of the frequency gain deviation of the antenna / feeder system.

The figure which shows the standing wave ratio characteristic of the antenna The figure which shows the standing wave ratio characteristic of the antenna Diagram showing frequency characteristics for subcarriers Diagram showing frequency characteristics for subcarriers Diagram showing frequency characteristics for pilot subcarriers The figure which shows the OFDM system structure of this invention The figure which shows the structure of the control part of 1st Embodiment. The figure which shows an example of a modulation system conversion table The figure which shows the control procedure of the processor of 1st Embodiment. The figure which shows the control procedure of the processor of 1st Embodiment. OFDM system configuration of the second embodiment The figure which shows the structure of the control part of 2nd Embodiment. The figure which shows the control procedure of the processor of 2nd Embodiment. The figure which shows the control procedure of the processor of 2nd Embodiment.

Explanation of symbols

1 Serial / Parallel Converter 2 Modulator 2
3 Inverse Fourier Transform Unit 4 Guard Interval (GI) Unit 5 Digital / Analog Conversion (D / A) Unit 6 Final Amplifier 7 Antenna Element 8 Antenna Element 9 Analog / Digital Conversion Unit 10 Guard Interval Unit 11 Fourier Transform Unit 12 Demodulation Unit 13 Parallel / Serial Conversion (P / S) Unit 14 Control Unit 15 Gain Control Unit 16 Modulation Method Conversion Table 17 Bus 18 Input Interface 19 Processor 20 Modulation Unit Control Unit 21 Gain Control Unit Control Unit 22 Antenna Table 23 Opposite Station

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The configuration of the embodiment is an exemplification, and the present invention is not limited to the configuration of the embodiment. In the following embodiment, the embodiment will be described using OFDM transmission (including OFDMA) as an example of frequency division multiplexing transmission. However, this embodiment may use other frequency division multiplexing transmission using a plurality of subcarriers. it can.

  Examples of frequency characteristics with respect to the signal level when performing OFDM transmission are shown in FIGS. In FIG. 3 to FIG. 5, as an example, it is an OFDM signal using 20 subcarriers. 3 to 5, the number of each subcarrier starts with the subcarrier C01 on the lowest frequency side, and the subcarrier on the highest frequency side is C20. Subcarriers C01, C06, C11, and C16 indicated by bold lines indicate pilot carriers. The pilot carrier is a subcarrier used for communication control. A plurality of pilot carriers can be provided adjacent to each other.

  FIG. 3 shows the characteristic when the SWR characteristic with respect to the frequency of the antenna / feeder system is flat and the output power of each subcarrier is the same. That is, FIG. 3 shows the frequency characteristics of each subcarrier in an ideal state of the antenna / feeder system. FIG. 4 shows the frequency characteristics of each subcarrier output from the actual terminal station 24. FIG. 4 is a characteristic obtained by adding the loss of the antenna / feeder system of FIG. 1 to the characteristic of FIG. In FIG. 4, C09 is the subcarrier with the highest signal level. The signal level decreases as the frequency goes from C09 to low and high frequencies. FIG. 5 shows pilot carriers C01, C06, C11, C16 and subcarriers C02 to C05 extracted from the characteristics shown in FIG. The following can be understood from the characteristics shown in FIG. The average value of the carriers C01, C06, C11, and C16 is the signal level of b. The signal levels of pilot carriers C01 and C16 are c, which is lower than the value of b. The signal levels of the pilot carriers C06 and C11 are a that is higher than the value of b.

  That is, it is possible to eliminate the influence of the frequency gain deviation of the antenna / feeder system by considering the difference from the value of b at the frequency position of each subcarrier.

  Specifically, a frequency multiplex transmission apparatus that transmits and receives a frequency multiplex signal including a plurality of subcarriers is opposed to a transmitter capable of transmitting the frequency multiplex signal by a plurality of modulation schemes and a signal state for the frequency multiplex signal. A receiving unit capable of receiving from a station, a control unit for obtaining a signal state for each subcarrier based on the received signal state and the frequency characteristics of an antenna in the transmitting unit, and performing transmission control based on the obtained result; Is provided.

  Here, the transmission control means selection of a modulation scheme and adjustment of transmission power in accordance with the signal state of each subcarrier. The modulation method selection will be described as a first embodiment, and transmission power adjustment will be described as a second embodiment.

[OFDM system of the first embodiment]
A first embodiment for realizing the above will be described below. The first embodiment is an example in which the selection of the subcarrier modulation scheme is controlled by adding the loss of the antenna / feeder system.

  The OFDM system configuration of the first embodiment is shown in FIG. The terminal station 24 is a terminal station as a wireless communication device. In the transmission unit of the terminal station 24, serial / parallel conversion (S / P) conversion is performed on the encoded (error correction encoded) input data by the serial / parallel converter 1. High-speed serial data is converted into a plurality of low-speed symbol strings by S / P conversion. These symbols correspond to each subcarrier. A modulation section 2 is provided for each divided symbol data series. The modulation unit 2 performs predetermined modulation (eg, 64QAM, 16QAM, QPSK). In this way, the first-order modulated signal is subjected to inverse Fourier transform in an inverse Fourier transform (IFFT) unit 3. This inverse Fourier transform can be regarded as a transformation from the frequency domain to the time domain. The guard interval (GI) unit 4 adds a GI to the inverse Fourier transformed signal to avoid intersymbol interference accompanying transmission. The symbol to which GI is added is converted into an analog signal by a digital / analog conversion (D / A) unit 5. The analog signal is added with a carrier wave and amplified by the final stage amplifier 6. The amplified analog signal is transmitted from the antenna element 7. Note that at least a plurality of pilot carriers are allocated among the plurality of subcarriers.

  The OFDM signal transmitted from the antenna element 7 is received by the opposite station 23 as a wireless communication device. The opposite station 23 demodulates the OFDM signal from the terminal station 24 by a receiver and measures the SNR of a plurality of pilot carriers allocated to subcarriers in the OFDM signal. Then, the opposite station 23 calculates the average SNR of a plurality of pilot carriers from the measurement result. The calculated SNR is transmitted from the opposite station 23 to the terminal station 24 as the signal state of the pilot carrier. The configuration of the opposite station 23 can be configured by a transmission unit and a reception unit having the same configuration as the transmission unit and the reception unit of the terminal station 24.

  In the reception unit of the terminal station 24, the incoming signal is received by the antenna element 8. The received signal is digitized by the analog / digital converter 9. The guard interval unit 10 removes the guard interval from the digitally converted signal. The signal from which the guard interval has been removed is subjected to Fourier transform in a Fourier transform (FFT) unit 11. The Fourier-transformed signal is demodulated by the demodulator 12 for each subcarrier. By demodulating by the demodulator 12, a data series corresponding to each subcarrier is obtained. These are converted by a parallel / serial conversion (P / S) unit 13 to obtain demodulated reception data. In the subsequent stage of the P / S unit 13, a decoding process necessary for data processing is performed.

  The control unit 14 in the terminal station 24 obtains subcarrier signal states from the received data using the SNR average values of a plurality of pilot carriers transmitted by the opposite station 23, and selects an optimum modulation method. Further, the control unit 14 sets the selected modulation scheme for the modulation unit 2. Specifically, the control unit 14 obtains an SNR value corresponding to each subcarrier from the average value of the received SNR and the frequency characteristic of the antenna, and performs control (adaptive modulation control) to vary the modulation scheme corresponding to the obtained SNR value. )I do.

[Configuration of Control Unit of First Embodiment]
The configuration of the control unit 14 of the first embodiment is shown in FIG. FIG. 7 shows a state in which the input interface 18, the processor 19, the modulation unit control unit 20, the antenna table 22 and the modulation method conversion table 16 are connected to the bus 17.

  The input interface 18 receives a signal from the parallel / serial conversion (P / S) unit 13 of FIG. Furthermore, the input interface 18 extracts the SNR average value of a plurality of pilot carriers transmitted by the opposite station 23.

  The antenna table 22 is a table that stores how many dB each subcarrier is deviated from the average value of the SNR of the pilot carrier. This table is obtained in advance by measuring the SWR characteristics of the antenna / feeder system. From the characteristics shown in FIGS. 4 and 5, the antenna table 22 is configured as a table indicating how much difference there is from the average value b of the pilot carrier at the frequency position of each subcarrier. As an example, in FIG. 5, C01 and C16 are 2 dB lower than the average value, and C06 and C11 are 2 dB higher than the average value. Thus, the antenna table 22 stores on the table how many dB difference is from the average value for each subcarrier.

  The modulation system conversion table 16 is a table that stores an optimal modulation system corresponding to the SNR. FIG. 8 shows an example of the modulation system conversion table 16. In FIG. 8, QPSK is selected in a state 803 (11 dB or less) where the SNR is bad, 16 QAM is selected in an intermediate state 802 (over 11 dB and less than 15 dB), and 64 QAM is selected in a state 801 (15 dB or more) where the SNR is good. Configure the table as follows.

  The processor 19 obtains an average SNR value of a plurality of pilot carriers from the input interface 18. Then, the processor 19 obtains an SNR estimated value that is a signal state of each subcarrier from the signal level difference for each subcarrier and the SNR average value of a plurality of pilot carriers from the antenna table 22. The processor 19 compares the obtained SNR estimation value of each subcarrier with the modulation scheme conversion table 16 and selects a modulation scheme.

  The modulation unit control unit 20 controls the modulation units 2 such that each modulation unit 2 performs modulation using the modulation scheme selected by the processor 19.

[Processing procedure of the processor of the first embodiment]
9 and 10 show the control procedure of the processor of the first embodiment. The overall control flow will be described with reference to FIG. First, the processor 19 performs step S10. In step S10, the processor 19 selects one subcarrier to be adjusted. This selection is sequentially performed according to a predetermined order. Next, the processor 19 performs step S20. In step S20, a predetermined transmission power is set for the subcarrier selected by the processor 19. Next, the processor 19 performs step S30. In step S30, an encoding modulation scheme is selected for the subcarrier selected by the processor 19. Next, when step S30 ends, the processor 19 returns to step S10 and selects a subcarrier to be adjusted again.

  FIG. 10 shows the flow in step S30 of FIG. First, the processor 19 performs step S31. In step S31, the processor 19 reads the signal level difference corresponding to the subcarrier selected in step S10 from the antenna table 22. This signal level difference is a value based on the frequency characteristics of the antenna / feeder system.

  Next, the processor 19 performs step S32. In step S <b> 32, the processor 19 acquires the average value of the pilot carrier from the input interface 18.

  Next, the processor 19 performs step S33. In step S33, the processor 19 calculates an SNR value obtained by adding the signal level difference of the subcarrier acquired in step S31 to the SNR average value of the pilot carrier acquired in step S32.

  Next, the processor 19 performs step S34. In step S34, the processor 19 refers to the modulation scheme conversion table 16 using the SNR value calculated in step S33. Then, the processor 19 selects a modulation method based on the comparison result.

  Next, the processor 19 performs step S35. In step S35, the processor 19 instructs the modulator control unit 20 to set the modulation method selected in step S10 in the modulator 2.

  Thereafter, as described in the control of the modulation unit control unit 20 in FIG. 7, the modulation unit control unit 20 controls the modulation unit 2 so as to perform modulation using the modulation scheme selected by the processor 19.

A specific example of modulation scheme control will be described using subcarrier C02. In FIG. 5, a is 2 dB higher than b, and c is 2 dB lower. Therefore, C02 is a value between b and c (greater than -2 dB and less than 0 db). It is assumed that C02 is described in the antenna table as -1 dB. When the average SNR from the opposite station is 13 dB, the SNR of C02 is 13 dB-1 dB = 12 dB
It becomes. When Q02 is calculated (after correction), 12 dB is compared with the value in the table of FIG. 8, 16QAM is selected.

  In the first embodiment, since the opposing station is configured to send back the average of the SNR values of the plurality of pilot carriers, the antenna table 22 indicates the distance between the average values of the plurality of pilot carriers for the signal level of each subcarrier. Stored as a table. However, this embodiment does not necessarily need to use an average value of a plurality of pilot carriers. For example, when the opposing station 25 returns an SNR for a specific pilot carrier, a table indicating how far each subcarrier is from the specific pilot carrier may be used based on FIGS. 4 and 5.

  In the first embodiment, a plurality of subcarriers may be grouped. Then, the bands composed of a plurality of subcarriers grouped are set to different modulation schemes in accordance with the frequency selective fading situation. For example, in the group C01 to C05, the processor reads the signal level difference of the pilot carrier of C01, obtains the SNR of the pilot carrier of C01 based on this signal level difference, and selects the modulation method from C02 to C05. . In this way, it is possible to reduce the number of times of selecting a subcarrier modulation scheme.

  The second embodiment will be described below. The second embodiment is an example of saving transmission power in consideration of the characteristics of the antenna / feeder system when the modulation method is fixed.

[OFDM system of the second embodiment]
An OFDM system configuration of the second embodiment is shown in FIG. The terminal station 24 is a terminal station as a wireless communication device. In the transmission unit of the terminal station 24, serial / parallel conversion (S / P) conversion is performed on the encoded (error correction encoded) input data by the serial / parallel conversion unit 1. High-speed serial data is converted into a plurality of low-speed symbol strings by S / P conversion. These symbols correspond to each subcarrier. A modulation section 2 is provided for each divided symbol data series. The modulation unit 2 performs predetermined modulation (eg, 64QAM, 16QAM, QPSK). The gain of the signal modulated for each data series is controlled by a gain control unit 15 provided for each data series. In this way, the signal subjected to gain control is subjected to inverse Fourier transform in an inverse Fourier transform (IFFT) unit 3. This inverse Fourier transform can be regarded as a transformation from the frequency domain to the time domain. The guard interval (GI) unit 4 adds a GI to the inverse Fourier transformed signal to avoid intersymbol interference accompanying transmission. The symbol to which GI is added is converted into an analog signal by a digital / analog conversion (D / A) unit 5. The analog signal is added with a carrier wave and amplified by the final stage amplifier 6. The amplified analog signal is transmitted from the antenna element 7. Note that at least a plurality of pilot carriers are allocated among the plurality of subcarriers.

  The OFDM signal transmitted from the antenna element 7 is received by the opposite station 23 as a wireless communication device. The opposite station 23 demodulates the OFDM signal from the terminal station 24 by a receiver and measures the SNR of a plurality of pilot carriers allocated to subcarriers in the OFDM signal. Then, the opposite station 23 calculates the average SNR of a plurality of pilot carriers from the measurement result. The calculated SNR is transmitted from the opposite station 23 to the terminal station 24 as the signal state of the pilot carrier. The configuration of the opposite station 23 can be configured by a transmission unit and a reception unit having the same configuration as the transmission unit and the reception unit of the terminal station 24.

  In the reception unit of the terminal station 24, the incoming signal is received by the antenna element 8. The received signal is digitized by the analog / digital converter 9. The guard interval unit 10 removes the guard interval from the digitally converted signal. The Fourier transform (FFT) unit 11 performs Fourier transform on the signal from which the guard interval has been removed. The Fourier-transformed signal is demodulated by the demodulator 12 for each subcarrier. By demodulating by the demodulator 12, a data series corresponding to each subcarrier is obtained. These are converted by a parallel / serial conversion (P / S) unit 13 to obtain demodulated reception data. In the subsequent stage of the P / S unit 13, a decoding process necessary for data processing is performed.

  The control unit 14 in the terminal station 24 obtains an optimum gain from the received data using the average SNR values of a plurality of pilot carriers transmitted by the opposite station 23, and calculates the power of each subcarrier corresponding to the obtained SNR value. Perform variable control.

[Configuration of Control Unit of Second Embodiment]
The configuration of the control unit 14 of the second embodiment is shown in FIG. In FIG. 12, an input interface 18, a processor 19, a gain control unit control unit 21, an antenna table 22, and a modulation system conversion table 16 are connected to a bus 17.

  The input interface 18 receives a signal from the parallel / serial conversion (P / S) unit 13 of FIG. Furthermore, the input interface 18 extracts the SNR average value of a plurality of pilot carriers transmitted by the opposite station 23.

  The antenna table 22 is a table that stores how many dB each subcarrier is deviated from the average value of the SNR of the pilot carrier. This table is obtained in advance by measuring the SWR characteristics of the antenna / feeder system. From the characteristics shown in FIGS. 4 and 5, the antenna table 22 is configured as a table indicating how much difference there is from the average value b of the pilot carrier at the frequency position of each subcarrier. As an example, in FIG. 5, C01 and C16 are 2 dB lower than the average value, and C06 and C11 are 2 dB higher than the average value. Thus, the antenna table 22 stores on the table how many dB difference is from the average value for each subcarrier.

  The modulation system conversion table 16 is a table that stores an optimal modulation system corresponding to the SNR. FIG. 8 shows an example of the modulation system conversion table 16. In FIG. 8, QPSK is selected in a state 803 (11 dB or less) where the SNR is bad, 16 QAM is selected in an intermediate state 802 (over 11 dB and less than 15 dB), and 64 QAM is selected in a state 801 (15 dB or more) where the SNR is good. Configure the table as follows.

  The processor 19 obtains an average SNR value of a plurality of pilot carriers from the input interface 18. The obtained average SNR values of a plurality of pilot carriers are compared with the modulation scheme conversion table 16. A modulation method is selected based on the comparison result. The difference between the SNR average value of the pilot carrier and the required SNR of the modulation scheme selected by each subcarrier is calculated.

  The gain control unit control unit 21 controls the gain control unit 15 based on the calculation result of the processor 19. Specifically, a subcarrier with an excessive signal level decreases the gain, and a subcarrier with an excessive signal level increases the gain.

[Processing procedure of the processor of the second embodiment]
13 and 14 show the control procedure of the processor of the second embodiment. The overall control flow will be described with reference to FIG. First, the processor 19 performs step S40. In step S40, the processor 19 selects a coded modulation method. Specifically, as shown in FIG. 14 a, in step 41, the processor 19 obtains an average value of the pilot carrier SNR from the input interface 18. Further, in step 42, the processor 19 selects a modulation scheme from the average value of SNRs of a plurality of pilot carriers. Based on the selection result, the encoding modulation scheme of the modulation unit 2 is set.

  Next, the processor 19 performs step 50 of FIG. In step 50, a subcarrier for transmitting data to the opposite station 23 is selected.

  Next, the processor 19 performs step 60 of FIG. The difference between the SNR average value of the pilot carrier and the required SNR of the modulation scheme at the subcarrier selected at step 50 is calculated, and the gain of the subcarrier selected at step 50 is controlled.

  Specifically, as in step 61 of FIG. 14b, based on the antenna table based on the average value of the pilot carrier SNR and the characteristics of FIGS. 4 and 5, the modulation scheme of the subcarrier selected in step 50 is determined. The amount by which the required SNR is separated from the average value of the SNR of the pilot carrier is calculated.

  The above-described embodiments can be appropriately combined as necessary.

Claims (6)

In a frequency multiplex transmission apparatus that transmits and receives a frequency multiplex signal including a plurality of subcarriers,
A transmitter capable of transmitting the frequency-multiplexed signal by a plurality of modulation schemes;
A receiving unit capable of receiving a signal state for the frequency multiplexed signal from the opposite station;
A frequency comprising: a control unit that obtains a signal state for each subcarrier based on the received signal state and a frequency characteristic of an antenna in the transmission unit and performs transmission control based on the obtained result Multiplex transmission equipment.   2. The frequency division multiplex transmission apparatus according to claim 1, wherein the control unit comprises setting modulation of the data based on a result of a signal state for each subcarrier.   2. The frequency multiplex transmission apparatus according to claim 1, wherein the control unit controls a gain for each subcarrier based on a result of a signal state for each subcarrier.   2. The frequency multiplexing transmission apparatus according to claim 1, wherein the signal state is an average value of signal-to-noise ratios of a plurality of subcarriers.   5. The frequency division multiplex transmission apparatus according to claim 4, wherein the control unit selects a subcarrier to be controlled from the plurality of subcarriers, and the selected subcarrier has a difference from an average value of the signal-to-noise ratio. A frequency multiplex transmission apparatus, characterized in that control is performed based on a table storing whether or not there is. In a frequency multiplex transmission apparatus that performs frequency multiplex transmission using a plurality of subcarriers,
A serial-parallel converter for parallelizing transmission data corresponding to a plurality of subcarriers;
A modulation unit provided for each of the data corresponding to each subcarrier, and capable of modulating the data with a plurality of modulation schemes;
An output of the plurality of modulators and an inverse Fourier transform unit;
A transmission unit that transmits the output of the inverse Fourier transform unit as a radio wave from an antenna;
A receiver for receiving radio waves from the antenna;
A Fourier transform unit for Fourier transforming the signal from the receiving unit;
A demodulation unit provided for each of a plurality of outputs from the Fourier transform unit, and demodulating the plurality of outputs;
A parallel-serial converter for serializing outputs from the plurality of demodulation units;
A frequency multiplex transmission apparatus comprising: a control unit that controls a modulation scheme of each modulation unit based on a frequency characteristic of an antenna and a signal-to-noise ratio of a subcarrier.

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